Magnetron voltage control for arcs



Sept. 3, 1957 e. c. RICH MAGNETRON VOLTAGE CONTROL FOR ARCS Filed June 21, 1955 olc.

INVENTOR GERALD C. RICH ATTORNEY nited States Patent MAGNETRON VOLTAGE CONTROL FOR ARCS Gerald C. Rich, Los Altos, Calif., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application June 21, 1955, Serial No. 516,859

4 Claims. (Cl. 314-73) This invention relates to control mechanism sensitive to both the current through a load and the voltage drop across it.

As an exemplification of the invention, the control device is shown as applied to control the position of consumable electrodes, for example, carbon electrodes, which electrodes are utilized for search lights, pharos and picture projection equipment.

In such utilizations it is necessary to provide means for feeding the electrodes as they are consumed. In modern equipment, the electrodes are supplied with direct current and the electrodes are moved toward each other by motor driven rollers, the motor being under control of a relay either in series or in shunt relation with the electrodes. However, the arc voltage and current varies very little from a fixed value as the arc gap changes in length although the light intensity at a desired focal point does vary greatly with these changes. It has been found that by sensing both the current and voltage variations by a device which can integrate these variations, much more sensitive control over the length of the arc gap and therefore, the light intensity at a given focal point, may be exercised. Furthermore, the series or shunt relay as used in previous arc controls must close or open at particular values of current or voltage and the ditterential between the closing current and the drop-out current is some practical minimum but finite value. Therefore, the arc current could deviate considerably from the most efiicient operating point before the control is effective. In addition, the adjustment of the relay for best operating point is critical. In accordance with this invention, any relay designed for operation at a current amply below the operating current of a diode in series with the relay is satisfactory, since, by reason of operation of the diode, the relay either has full current or zero current and setting of the relay is not critical.

It is an object of this invention to provide a system of control whereby regulation may be effected in response to both current and voltage conditions.

It is a further object of the invention to incorporate with such a system an element which shall be capable of responding, in an integrating sense, to both voltage and current conditions in a circuit.

It is a still further object of the invention to utilize a diode in series with a relay to control the feed of arc electrodes.

These and other objects will be apparent after reading the following specification and claims when considered in conjunction with the accompanying drawings which illustrates an embodiment of the invention.

In said drawing, at 10, 12 there are represented positive and negative carbon electrodes with an arc gap 14 therebetween. Conventional roller drive means 16 is employed to cause the electrodes to be moved toward or from each other, these being driven, through appropriate reduction gearing, by a reversible motor 18. The reversible motor may be of the current lead interchange- 2,8 i5558 Patented Sept. 3, 1957 ICC able brush type with its field 20 connected across the direct current lines 22 and 24 and the brushes connected to these lines via a conventional reversing relay 26. The coil 28 of the relay is connected at one end, as at 30, to one of the D.-C. lines, as line 24, and at its other end to a switch diode 32 similar to a magnetron, and through the switch diode to a point 34 on the other line. The connections of the coil and switch diode to the line are such as to directly sense the voltage across the gap 14.

The switch diode 32 comprises a non-magnetic metal or ceramic casing 36 insulatingly supporting a cathode sleeve 38 and a parallel anode 40. Cooperative with the diode 32 is a generally C-shaped electromagnet 42 whose poles 44 and 46 approach each other and lie close to a plane through the diode electrodes. The flux from the magnet poles is at right angles to the electron stream and reacts with the flux surrounding the electron sheet to deflect the same more or less depending on the strength of magnetic flux and strength of current fiow through the diode, as controlled by the voltage applied to it.

The coil 48 of the electromagnet is in series with the line and the electrodes so that the magnetic flux developed across the tips 44, 46 is a function of the current fiow across the are 14. To steady the current flow through the magnet coil and carbon electrodes a series impedance Z, indicated by the numeral 50, is provided, and to abate hunting action of the relay 26, a heavy capacitor 52 bridges the coil 28 of the relay. The diode is here pictured in its simplest form. In actual use, a standard concentric magnetically controlled cylindrical diode or magnetron would be used in which the current can be cut ofi abruptly at a critical value of the magnetic field.

The arrangement operates in this fashion: When the carbon electrodes are separated and the arc is extinguished there is no current flow through the coil 48 and consequently electrons emitted from cathode 38 are not inhibited from reaching the anode 40 by any action of the electromagnetic flux in the electromagnet 42. Also the potential across the arc is now line voltage, and substantially that voltage is also existent across the diode. As a consequence, a maximum number of electrons emitted from the cathode will strike the anode, and the control circuit comprising the diode 32 and relay 26 will be closed. It should be noted that the current and voltage conditions are algebraically additive in establishing the control circuit thereby making the control very sensitive. Closing of the relay will cause current to flow through the motor armature in a direction to move the carbons toward each other until they come into contact.

When these carbons do contact each other, maximum current flow in the coil 48 of the switch diode is established, while the voltage across the diode is at a minimum. Now the fiux through the electromagnet 42 is at a maximum so as to cause maximum deviation of the electron stream between cathode and anode and diminishing the current flow through the diode to such an extent as to allow the series connected relay 26 to drop out. Here, again, current and voltage conditions are such as to cause the arc effects to be cumulative on the diode. Dropping out of the relay causes the current though the motor armature to reverse, reversing the motor and separating the carbons until the operating point is reached, thus striking the arc. The motor will then be operative as the carbons are consumed to cause the carbons to approach or, if necessary, recede from each other, under control of both the current and voltage conditions existing at the arc. Any suitable anti-hunting control may be utilized with the reversing apparatus; capacitor 52, across the coil 28, or a short circuiting copper ring about part of the laminations of the relay core are merely exemplary of what may be employed for this purpose.

Having thus described the invention, what is claimed 1s:

1. In combination with a load subject to current and voltage variations, and normally operative at a predetermined current and voltage, means to maintain said load at the predetermined value of current and voltage comprising a switch diode, an electromagnet having pole pieces associated with the diode to cause a magnetic flux to flow at right angles to the electron stream within the diode, the coil of the electromagnet being in series with the load and the electrodes of the diode being in shunt relation with the load, and means under control of the current flow through the diode to vary the current and voltage conditions of the load.

2. In combination with a load subject to current and voltage variations, and normally operative at a predetermined current and voltage, means to maintain said load at the predetermined value of current and voltage comprising a switch diode, an electromagnet having pole pieces associated with the diode to cause a magnetic flux to flow at right angles to the electron stream within the diode, the coil of the electromagnet being in series with the load and the electrodes of the diode being in shunt relation with the load, and means under control of the current flow through the diode to vary the current and voltage conditions of the load, said means comprising a relay in series with the diode, a load resistance varying device and means under control of the relay contacts for controlling the action of said device.

3. In combination with a load subject to current and voltage variations, and normally operative at a predetermined current and voltage, means to maintain said load at the predetermined value of current and voltage comprising a switch diode, an electromagnet having pole pieces associated with the diode to cause a magnetic flux to flow at right angles to the electron stream within the diode, the coil of the electromagnet being in series with the load and the electrodes of the diode being in shunt relation with the load, and means under control of the current flow through the diode to vary the current and voltage conditions of the load, said means comprising a relay in series with the diode, a motor for varying the load, a load feed line and connections between the relay contacts, the load feed line and the motor.

4. A consumable electrode feed mechanism for are lights and the like, comprising electrode feeding devices, a reversible motor for driving the devices, a relay having contacts controlling the direction of motion of the motor, said relay also having a coil, a diode in series with the coil, an electromagnet associated with the diode to control the flow of electrons therein, said electromagnet having a magnetizing winding, said magnetizing winding being in series'with the electrodes, and said series connected diode and relay coil being in shunt with the electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 

